Development of a cold-active microbial compound biofertilizer on the improvement for rice (oryza sativa L.) tolerance at low-temperature

The use of plant growth-promoting bacteria has been used to improve low-temperature stress in agriculture. However, the use of cold compound biofertilizers is not widely used to reduce the application of chemical fertilizers. In this study, a compound biofertilizer was developed to improve the tolerance of rice (Oryza sativa L.) to low-temperature stress, containing six cold-tolerant bacteria that were isolated from wild rice rhizosphere, with following capabilities: solubilization of phosphate and potassium, fixation of nitrogen, production of indoleacetic acid, ammonium, hydrogen cyanide, and siderophores. The results indicated that seed inoculation significantly increased germination (25%) and promoted root (84.34%) and shoot (54.61%) growth compared to the control. In seedlings, the inoculation significantly increased (P < 0.05) the shoots length (69.11%), roots (110.12%), and plant biomass; in addition, a significant accumulation of chlorophyll (83.74%), proline (285.98%), soluble sugar (471%) and soluble protein (112.5%) was detected compared to the non-inoculated control. It also considerably improved protection against oxidative stress by lowering malondialdehyde content (127.93%) lower than control, increasing antioxidant enzymes, and higher accumulation of nitrogen, phosphorus, and potassium in plants compared to control. The biofertilizer application composed of phosphate solubilizing, potassium solubilizing, and nitrogen-fixing bacteria proved an effective alternative to improve cold stress in rice. Its effect was significantly better than the commercial products used in the study. Its use can be extended as an alternative to reduce chemical fertilization and contribute to the development of sustainable agriculture.